Solid electrolytic capacitor with planar cathode lead

ABSTRACT

The invention refers to a solid electrolytic capacitor, the anode and cathode leads of which are in known manner formed from a metal strip while the electrolytic capacitor per se comprises a metallic anode body which has a relatively large plane surface above which a dielectric layer and a cathode layer are stacked in that order. The cathode lead is a part formed from the metal strip and shaped as a plate having a surface that is at least as large as the plane surface of the anode body and faces the cathode layer.

This is a continuation of application Ser. No. 429,950, filed Jan. 2,1974 and now abandoned.

The invention refers to a solid electrolytic capacitor, the anode andcathode leads of which are in known manner formed from a metal strip.

In solid electrolytic capacitors the anode is usually produced fromtantalum powder sintered into a cylindrical body in which a tantalumlead is embedded to constitute an anode electrode. The anode body iselectrically oxidized to form a dielectric layer and is thereafterimpregnated with, for example, manganese nitrate which is pyrolyticallyconverted to manganese dioxide to form a semiconducting layer which isprovided with a cathode electrode by applying a further layer of silverlac.

A conventional procedure for producing an anode lead is to weld asolderable lead to the tantalum lead while a cathode lead is produced bywelding or bonding with conductive silver lac a likewise solderable leadto the silver lac of the cathode electrode. This procedure is simple andunexpensive but has the drawback that the contact surface between thecathode lead and the cathode electrode becomes small resulting in a highand eventually unstable series resistance. Attempts to increase thecontact surface by for example welding an extra plate to the cathodelead complicates the fabrication and increases the costs.

A cathode lead can also be produced by mounting the electrolyticcapacitor in a metal casing to which an electrical contact is obtainedby means of welding or applying silver lac. In this case a solderablelead is welded to the metal casing. This procedure in neither simple norunexpensive and is in resemblance to the earlier described proceduresdifficult to carry out by automatic machining.

According to a later developed procedure described in the U.S. Pat. No.3,646,404 the anode and cathode leads of the electrolytic capacitor areformed by punching or etching a solderable metal strip. This procedureis especially intended for automatic machining but the contact surfacebetween the cathode lead and the cathode electrode is small whichresults in a high series resistance. Furthermore, the punching oretching of the metal strip must be adjusted to new dimensions when thesize of the capacitor is changed which is a drawback in the fabrication.

The invention refers to a dry electrolytic capacitor in which the seriesresistance between the cathode lead and the cathode electrode is low andthe anode and cathode leads are formed from a metal strip without anyadjustment to new dimensions when the size of the capacitor is changed.The invention is characterized as it appears from the appended claimsand will be described more in detail in connection with the accompanyingdrawing in which FIG. 1 shows a perspective view of the electrolyticcapacitor according to the invention in a production phase just beforeencapsulation; FIGS. 2 and 3 show a schematic front view and side viewrespectively of the electrolytic capacitor in FIG. 1 afterencapsulation, and FIGS. 4 and 5 shows a front view and a top viewrespectively of the completed electrolytic capacitor.

FIG. 1 shows a perspective view of the solid electrolytic capacitoraccording to the invention in a production phase just beforeencapsulation. A capacitor element 1 has an anode electrode consistingof a tantalum lead 2 which is sintered into a rectangular anode body ofsintered tantalum powder. The surface of the anode body is in knownmanner electrolytically covered with a dielectric layer of oxide, asemiconducting layer of manganese dioxide being pyrolytically obtainedfrom manganese nitrate and on top of this a conductive silver lac layerconstituting the cathode electrode.

One surface of the capacitor element 1, that is plane as the underlyingsurface of the rectangular anode body, and the tantalum lead 2 areattached by means of a drop of silver lac to a plate 3 and by welding toa tab 4 respectively of a copper strip 5 which is advanced step by stepduring the production process. A new capacitor element 1 is attached tothe copper strip 5 each time it is advanced one step. The plate 3 isdisplaced laterally by bending it so that the tab 4 will receive thetantalum lead 2 in the appropriate position for welding.

FIGS. 2 and 3 show a schematic front view and side view respectively ofthe electrolytic capacitor in FIG. 1 after encapsulation in a plasticcasing 6. The broken lines of the copper strip 5 mark where this will bepunched to separate the electrolytic capacitor and produce the leads 7and 8 to the anode and cathode of the capacitor element through theplate 3 and the tab 4 respectively.

It is seen that a large contact surface and hence a low seriesresistance is achieved between the cathode lead 7 and the cathodeelectrode owing to the fact that the capacitor element 1 and the plate 3have plane contact surfaces. Furthermore, the width and lengthdimensions of the capacitor element 1 and hence the magnitude of thecapacitance can be varied within limits without requiring the punchingof the copper strip 5 to be adjusted to new dimensions. In this case acondition to be fulfilled is that the plate 3 shall have a surface atleast that large as the opposed surface of the capacitor element 1.

FIGS. 4 and 5 show a front view and a top view respectively of thecompleted electrolytic capacitor, the leads 7 and 8 of which are formedby punching the copper strip 5, and the front surface of plastic casing6 being provided with marking of the capacitance and maximal workingvoltage. The top of the plastic casing 6 has a recess 9 above the anodelead to make it easy to identify when the electrolytic capacitor isassembled.

We claim:
 1. An electrolytic capacitor comprising an anode body oftantalum in the form of a parallelepiped having six rectangular andplanar surfaces, one of said surfaces being covered with a dielectriclayer, a planar cathode layer of conductive material covering saiddielectric layer, a wirelike anode conductor of the same material assaid anode body extending outward from the central portion of another ofsaid surfaces which is perpendicular to said one planar surface, theaxis of said wirelike anode conductor being perpendicular to said othersurface, an anode lead and a cathode lead both having a laminarconfiguration, said anode lead being connected to said wirelike anodeconductor, in such a way that the plane defined by said wirelike anodeconductor and said anode lead lie in a plane parallel to the plane ofsaid one planar surface and the axis of said wirelike anode conductor isorthogonal to the axis of said anode lead, said cathode lead being bentinto three sections wherein the first and second outer sections aremutually parallel and the intermediate section making angles therewith,said first outer section being coplanar with said anode lead and saidsecond outer section being coplanar with and affixed to said one planarsurface of said anode body.